1. Field of the Invention
This invention relates generally to optical wireless communication links, and more particularly, to a method of aligning optical wireless transceivers having distinct mirrors for transmitting and receiving.
2. Description of the Prior Art
FIG. 1 illustrates an optical wireless link (OWL) system 100 consisting of two stations 102, 104, in which each station 102, 104 contains an optical transmitter 106, 114 and an optical receiver 108, 116 respectively. FIG. 2 illustrates the optical components associated with a single OWL transceiver 102. Transceiver 102 can be seen to include a laser transmitter 106 and a MEMs mirror 120 for directing a transmitted beam toward a remote station 104. Although existing OWL devices are not equipped with a MEMS mirror for directing an incident beam to a receiving element, transceiver 102 also has a receiver 108 and a MEMs mirror 122 for directing an incident beam to a receiving element 121 (likely through optional magnifying optics 123) in the transceiver 102.
FIG. 3 shows an OWL receiver and an OWL transmitter including the respective field of view 124 and beam divergence 126. Looking again at FIG. 2 and considering an existing OWL device, mirror 120 directs the transmitted beam toward the remote receiver 116, which must be oriented such that its field 124 of view includes the transmitting mirror 120 in order to receive the transmitted beam. One of the limiting factors associated with modern optical wireless transceivers results from the constraint on the receiver that it have a wide field of view 124 in order to see the incident beam across a relatively large angle. A receiver with a narrow field of view 124 would allow optics to intensify the incident beam, significantly increasing the SNR and subsequently the operating range of the system 100. A narrow field of view however, requires either very accurate positioning of the transceivers 102, 104 (such that the incident laser beam falls within the field of view of the respective receivers 108, 116). Otherwise, some method of re-directing the incident beam to compensate for initial positioning error will be required. A mirror, such as 122 in FIG. 2, can be used to re-direct the beam allowing the desired narrow field of view; however, it must be positioned in the proper orientation in order for the system to function.
In view of the foregoing, it would be desirable and advantageous in the optical wireless communication art to provide a technique for simultaneously aligning the two sets of mirrors (local transmitting mirror and remote receiving mirror) such that light traverses a path from the transmitting laser 106 of the outbound mirror 120, through free space, off the inbound mirror of the remote station 104, and finally onto the receiving element in the remote station.